1. Field of Invention
The present invention relates to methods for measuring hysteresis curves and anisotropic energy, and more particularly to methods for measuring hysteresis curves and anisotropic energy of multilayer magnetic memory units.
2. Description of Related Art
As applications of magnetic components for everyday life grow day-by-day, developing various kinds of magnetic materials with better physical characteristics become the trend of fashion for researchers. Measuring the hysteresis curves and anisotropic energy of magnetic materials are important for differentiating their characteristics.
Conventional methods for measuring hysteresis curves include vibrating sample magnetometer (VSM) or the Kerr rotation angle by laser beam.
The measurement principle of VSM is to vibrate the magnetic sample near the coils, and determine the magnetic properties with the corresponding magnetic flux variations.
The measuring principle of the Kerr rotation angle by laser beam is either to magnetize the magnetic material with an applied external magnetic field, or spontaneously magnetize a ferromagnetic material, which makes the refraction index of the material magnetically birefringent. That means the refraction index of right-handed and left-handed polarized light are different. The magneto-optic Kerr effect will elliptically polarize a linearly polarized laser normally incident on a sample surface. The Kerr angle is the angle between the linearly polarized light and the elliptically polarized light. The direction of the magnetic moment could be determined using the angle of the elliptically polarized light, and together with the external magnetic field, the whole hysteresis curve can be obtained.
The conventional method for measuring the anisotropic energy of a single-layer uses an applied external magnetic field along the axis parallel to the direction of the sample magnetization to obtain the coercive field of the hysteresis curve and the variation curve of magnetization per unit of the sample. A second external magnetic field is applied along the axis perpendicular to the sample magnetization, wherein the intensity of the field must be much greater than the magnetization of the sample to obtain the variation curve of the perpendicular anisotropic energy of the sample. Software is then used to calculate the value of the anisotropic energy.
The aforementioned methods can all be affected by environmental factors. The VSM method is very sensitive. Any adjustment for the position between sample and coil will cause a significant deviation for the measurement. While measuring the Kerr rotation angle, a slight deviation regarding the pathway, intensity, or angle for the laser beam could also create some difficulty. The present invention provides methods that apply to the extra-ordinary Hall effect which can significantly reduce the difficulty to measure the hysteresis curves and anisotropic energy.
The conventional method can only measure the anisotropic energy of a single-layer material, however, if a magnetic structure consists of a plurality of magnetic materials, the conventional method fails to obtain the anisotropic energy of every magnetic material therein.
This other shortcoming for the conventional method is especially problematic for magnetic devices consisting of multi-film layers of various materials.